The present invention relates to a rolling bearing with a grease composition packed, more specifically, it relates to a rolling bearing having a good rust-preventive performance and the excellent flaking life, suitable for use in a high temperature, high speed, high load and high vibration condition, such as, an alternator and an intermediate pulley, and an electromagnetic clutch for an automobile air-conditioner as electric parts for an automobile or engine accessories.
In a rotation part of various power units of an automobile engine, such as electric parts for an automobile or engine accessories including an alternator, an electromagnetic clutch for an automobile air-conditioner, and an intermediate pulley, in general, a rolling bearing is used, and a grease is used as the lubricant therefor.
According to spread of FF cars aiming at a small size and a light weight as well as the demand to enlargement of the car room space, reduction of the engine room volume is inevitable, and thus a smaller size and a light weight of the above-mentioned electric parts and engine accessories are further promoted. Besides, a higher performance and a higher output are required to the above-mentioned parts. However, output decline is unavoidable by achieving a smaller size. For example, in an alternator and an electromagnetic clutch for an automobile air-conditioner, the output decline is compensated by a higher speed so that an idler pulley is made to have a higher speed accordingly. Furthermore, according to the demand for improvement of quietness, sealing of an engine room is enhanced. As a result, since the temperature inside the engine room is raised, the above-mentioned parts should be durable to a high temperature. According to the tendency toward the higher speed and higher performance, flaking accompanying the white structure change by the hydrogen brittleness can easily be generated in a bearing for the above-mentioned parts, and thus prevention thereof is a new important task.
Moreover, since the above-mentioned parts are often mounted in the lower part of an engine room, rain water, or the like, is often scattered thereon during a run. Therefore, a grease to be packed in a rolling bearing for these parts should have a rust-preventive performance superior to a grease to be packed in a rolling bearing to be used in other parts.
In order to provide a rust-preventive performance to a grease, in general, a rust-preventive additive is added. As a component of the rust-preventive additive, an inorganic passivating agent is often contained. In particular, a sodium nitrite is most effective, and thus it is the mainstream. Moreover, since the inorganic passivating agent is water-soluble but is hardly dispersed in an oil-based material such as a grease, a grease containing a surfactant is also commercially available. Furthermore, for example, JP-A-3-200898 proposes a grease provided by adding an oil-soluble organic inhibitor, a water-soluble inorganic passivating agent (sodium nitrite, or the like), and a rust-preventive agent made from a nonionic surfactant to a grease. (The term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d) However, although the sodium nitrite as the representative inorganic passivating agent has the excellent rust-preventive performance, it may be carcinogenic, depending on the application condition. Therefore, although it is not limited legally, it is preferable to avoid the use thereof. Moreover, a metal sulfonate as an organic inhibitor is used widely for its high rust-preventive ability, however, since it facilitates generation of a hydrogen as disclosed in Japanese Patent No. 2,878,749, it may cause generation of flaking by the hydrogen brittleness.
In view of the above-mentioned circumstances, the present invention has been achieved, and an object thereof is to provide a rolling bearing suitable for the use particularly under a high temperature, high speed, high load and high vibration condition, having a good rust-preventive performance and the excellent flaking life without a hazard to a human body.
As a result of the elaborate discussion for solving the problems, the present inventor has found out that a naphthenate and a succinic acid derivative are effective as a rust-preventive additive, and achieved the invention.
That is, the object can be achieved by a rolling bearing according to the invention, comprising an inner race, an outer race and rolling elements, with a grease composition comprising, as the main components, a base oil, a thickener and at least one kind of a rust-preventive additive made from a naphthenate or a succinic acid derivative, packed in a bearing space formed by at least the inner race, the outer race and the rolling elements, said at least one kind of a rust-preventive additive is present in an amount of 0.1 to 10% by weight based on the total amount of the grease composition.